Automatic telephone system



Aug. '24 1926.

, 1,597,032 J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM Original ile pril 5. "1921 4 shuts-shin. 1

I '-fmran or Jrlhn EEard'nar J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM ori i a Filed April 5. 1921 4 Shoots-Shoot 2 amt/r50 [.0155 PRIVATE umss Aug. 24 1926.

J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM Original Filed April 5. 1921 4 sheets-$11551; s

Juhn-EEardhsr Aug. 24 1926.

, J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM on inal Filed April 5.

1921 4 Sheets-Sheet 4 John EEa'rd nsr' a a stares iPiaTENIQFFICE-Q Jenn n. GARDNER, on onrcaso, iLLrnoIs, Assrcnon. BY MESN ASSIGNME TS, To AUTOMATIC ELECTRIC Inc, cnzcaeo. tumors, at c-onroaa'rron or DELA WARE.

'AUTOMATIG rnnnrzzcnn sYsTEM.

Application filed. April 5, '1921, Serial No. 458,973. Renewed December 1 2, i925 The present invention relates in general to autoinatlc telephone systems but is more particularly concerned with systems of the type usually installed in factories, mercantile establishments, and the like, such systems being commonly known as privateautoinaticexchanges.

More specifically the invention contemplates an improvement in what is known transfer or passing call service. This seriite, as is well known, supplies rneans whereby when a calling subscriber in the main exchange extends a connection to a sub scriber in the private automatic exchange, the calledsubscriber may, by operating his calling device, transfer or pass the callto thev line of another subscriber in the branch a I v duplicated in both connector switches conr men and by so arranging the circuits that these common relays perform their functions tor both connectors. A second object of the invention is to give an improved torm of supervision to an operator whereby she is positively notit'sed when the called subscriber answers and when disconnection is effected. The man ner in which these and other results are accomplished will. be described fully hereinafter with reference to the accompanying drawings.

Referring now to the drawings. in Fig. l. is shown trunk line incoming to the branch where it terminates in the main I l ronne-ctor l-l. This trunk line is of the o type and is adapted to be seized y the local selector connector repeaters of mi known construction. The conductors 10:2., inclusive, are the multiples of the trunk line comp ising conductors 5 and 6 which terminate in bank contacts in the outgoing. level of these local switches. The

main connector is of the well knownswitches Strowger vertical and. rotary type having the usual set of 100 contacts arranged in ten This connector has access rows or levels. to local subscribers hnes such as the one shown at substation A. Substation A isot the usual automatic constructionhaving the rotary lineswitch C individual to it.

In Fig. 2 at i-l is shown the auxiliary connector which is associated wrththe switch shownat H. The auxiliary connector H is s milar to the connector '11 and has access in the same manner to local subscribers lines such as that of the substation 'A m I his substationis similar to the one shown at A and also has the individual line switch C associated with it. j

Figs. 3 and 4 show a certain modification of the invention which is adapted to be used when two called subscribers are'desired on the line at one time: Substations A and A are called 'substationssimilar to'the substation A, and having the individual line C and C associated with them. In *5 is shown the manner in which the test contacts of: the connector switches are connect-ted in order to secure rotary service, that is, to enable the connector switches to be able to pick out an idle line in a group of lines or'it all lines in the group are busy to return the busy signal to the calling sub scriber.

Having briefly described the apparatus tion of the same will now be explained. For thi'sjpurpose it will be assumed that a calling subscriber in the inain exchange dcsires to call the subscriber at substation A shown in the drawings, the detailed operain the branch exchange and'that'he hasoperated various selectors and a selector repeater in the main exchange in order to connect with an idle trunk line extending to the private automatic exchange which, we

slow acting release relay 200 toabatteryg,

Relay 200 upon operating, at its armature 216 prepares the operating circuits of the main connector H,'at armature 215 places ground on release trunk conductor 115, and at armature 217 places ground on release trunk conductor 101 which extends ,to multiplied test contacts in the banks of the local connector selector repeaters whereby the incoming trunk line comprising conductors 5 and 6 is prevented from being seized by avlocal subscriber.

The calling subscriber in the main exchange mayanow operate his calling device in ac cordance with the next :digit of his desired number. By this operation a series of interruptionsiis produced in the circuit of the line relay 1 1 of the main connector H which deenergizes a plurality of times in response thereto.= At eachdeenergization an impulse of current is sent over the following path: Ground by way of, armature 30 and its back contact, conductor 110, armature 216 and its front contact, conduct r 119, off normal springs 7 1 and 73, winding of the vertical magnet 60, back contact and armature 4 T, conductor 122 and thence through the wind ing of the slow acting relay 202 to battery. Upon the first vertical step of the connector H, the off normal springs are shifted and the remaining impulses to the vertical magnet traverse adifferent circuit which is the same as the one previously traced except that itincludes the off nor mal springs 74; and 75, conductor 118, armature 226 and its front contact, and conductor 117, relay 202 being new in an operated position. The've-rtical magnet '60 operates to raisethe switch wipers 83, inclusive, step by step until they are )lElCGCl 0ppositethe level of bank contacts in which is located the contactset associated with the line of the substation A. The slow acting relay 202 is energized in series with the vertical magnet and retains its armatures attracted throughout the vertical movement of the switch and at the termination thereof decnergizes and transfers the operating circuit to the rotary magnet 61.

Thecallin-g subscriber in the 111511116X- change may now operate his calling device in accordance with the next and final digi of his desired number. As before,-another series of interruptions is produced in the circuit of the line relay 1& which deener gizes a corresponding number-of times. At each retraction of its. armature 80, an impulseof-current iszsent to the rotary magnet 61 over a circuit extending from ground by way of armature 30and-its back contact, conductor 110, armature 216 and its front contact, conductor-119, off normal springs" 74 and 17,5; conductor 118, armature 226 and its back contact, conductor; 120, nfiorking' contact of-ofijnofrmal spring-'71 and the said sprlngyycondnctor 121, back contact" and armature 230, at which point the circuit divides, one path extending through the winding of the slow acting relay 20 1 and thence to battery by way of armature 220 and its back contact, and the other path eX-V tending by way of conductor 135, armature e19 and its hack contact, and thence through the rotary magnet 61 to battery The retary magnet 61 operates to rotate the switch wipers SW83, inclusive, into engagement with the bank contacts associated with the line of the substation A which, wewill assume, are the bank contacts 91-9el, inclusive. The slow acting relay 20 1 is energized in multiple with the rotary ma-gnet and operates its armature 237 to connect the test wiper 82 with the winding of the test relay 203.

lit will first be assumed that'the line of desired substation is busy atthis time nder these conditions there will be a 'i'ound potential present upon the-test contact engaged by the test wiper 82 and a.

circuit will be completed extending from the said grounded test contact, by way of test wiper 82, conductor 1 10, armature 237 and its front coutact, and thence'through the winding of the test relay 203 to battery. The relay 203- is energized over this circuit and upon operating, establishes a locking circuit for itself at armature232 which extends from ground on release trunk co ndue-tor 115, off normal spring 70 and its working contact, conductor 114:, off normal spring 268 and its resting contact, normally closed springs controlled by armature 225, armature 232 and its front contact, normally closed springs controlled by armature 237, and thence through tne winding of the test relay 203; to battery. Another result of the onergization of relay 203 is that the busy tone is applied to the line ofthe calling subscriber overa circuit. extending fromthe busy machine by way of front contact and armature 283, armature 227 and its back contact,-conductor 126, and thence to the lower trunk conductor 6. This tone is audible to the calling subscriber and he will replace his r ceiver upon the switchhook thereby opening the circuit'o'f the line lit) relay 1% in the main connector H which in'nnediat-ely deenergizes opening the circuit of the slow acting relay 200. Relay 200 upon deenergizing, completes a circuit extending from ground byway of armature 30 and its back contact, conductor 110, armature 216 and its back contact, conductor 116, 011 normal spring 72 and its working contact, and thence through the winding of the release'inagnet 62' to battery. The release magnet 62 operates to restore the main connector H to -normal. Upon ground being removed from the release trunk conductor 1 115 at armature 215 cfthe slow= acting re lease'relay 200 the locking cireuitof the the winding of the stepp test relay 203 is opened and, this relay consequently deenergizes.

The above is the normal operation of the connector H when a busy lineis called protherefore ground will be present upon both these test contacts.

The 7 operation in this case is somewhat different from that above described and will now be explained. When the test relay 203 energized it prepared .a circuit for the stepping relay 201 at armature 231. Then, following the deenergization of the slow acting relay 204, a circuit is effective extending from ground on test contact 92, by way of test wiper 81, arma ture 46 and its back contact, conductor 137, armature 235 and its back contact, conduc: tor131, armature 51 and its back contact, armature 7 9 and its back contact, conductor 133, front contact and armature 231, through relay 201 and of the slow actthence through the wind; ing relay 202 to battery. and 202 are energized over this circuit. Relay 201 upon energizing, establishes a lock: ing circuit for itself at armature 213 and at armature 219 completes the rotary magnet circuit over the path extending from ground by way of front contact and armature 219,.

conductor 135, armature 49 and its back contact, and thence through the winding of the rotary magnet 61 to battery. The

rotary magnet 61 operates to rotate the,

switch wipers -83, inclusive, into engagement with the next set of bank contacts. It

will be seen that the slow actin rela 20 1 is not ener ized in multi le with the rotar magnetat this time as its circuit is broken at armature 220 of the stepping relay, 201. The rotary magnet 61 upon operating also opens the locking circuit of the relays 201 and 202. Relay 201 upon deenergizing, opens the circuit ofthe rotary magnet. V The further operation of the connector H depends upon whether or notthe line with which the switch wipers are now associated is or is not busy. If busy, there will be a ground potential present upon the test' stepping relay 201 and the rotary magnet 61 will continue until an idle line is found or until the switch wipers 8083, inclusive, are rotated lnto. engagement with the last The relays 201 line of the group. If rotated into engagev .ment' with the last-contact set of the groul there will be a ground potential onlypresent upon the test contact engagedby test wiper '82, the test relay 203 will be maintained energized, but the steppingrelay 201-will not lie operated. A busy tone will .now be given to the calling subscriber in the same manner as was before described.

It will now be assumed that the line of gaged by the test wiper 32 and no circuit will 51 be completed for the test relay 203. Then, following the deenergzation of the slow acting relay 20%, a circuit is completed en- .cnding from ground on release trunk conductor 115, off normal spring 70 and its working contact, conductor 11 1, oif normal spring 268 and its resting contact, normally closed springscontrolled by armature 225, armature 232 and its back contact, conductor 133, upper winding of the switching relay 16, back contact and armature 18, conductor 136-, back contactand armature. 237, conductor 140, normally closed springs controlled by armature 53, test wiper 82, test oontact 93, through the winding of the switching relay'96 of the individual line switch 0, and thence through the winding of the mag net 97 to battery. The relays 16 and 96 are ener ized over this circuit. However, due vto a mechanical interlocking device controlled by the armature of the line relay which is now normalthe relay 96 is only operated enough to disconnect the linev of the substation A from its normal battery and ground connections'in the line switch C. Bela 16 u on ener 'izin' establishes y 7 a a a locking circuit for itselfat armature 50 which extends from groundon release trunk I called substation until an answer is obtained.

V w hen this occurs :the ring out 0H relay 15 will be energized over the called snbscribefs line loop. Upon operating, this relay at armature 36 establishes locking. circuitfor itself and at armatures 3 1 and 39 opens the ringing circuit and at the front contacts. of these armatures finally completes the talking connection. The back bridge relay 13 is energizedorer the called snbscribers line loop and upon operating, core the callingand called subscribers, battery being supplied to the calling party in the main exchange the windings of the line relay of the selector repeater and to the called subscribers line from the windings of the back bridge relay 13. When the conversation is terminated both subscribers will replace their receivers upon the switchhoolrs and the release of the main connector ll. will be accomplished when the subscriber at the calling substation in the main e1:-

change replaces his reccr'er in the same manner as was describedhereinbefore.

lVhen the called subscril er at substation A answers he may find it necessary to transfer the calling subscriber to some other party in the private automatic exchange. such as the subscriber at substation A]. In order to do this he will operate his calling device for the digits of that local subscribers number. By this operation a series of interruptions is produced in. the circuit of the back bridge relay 13 which deenergizes a plurality of times in response thereto. At each retraction of its armature 27, an impulse of current is sent over the following circuit: From ground by way of armature 27 andits back contact, armature 2G and its front contact, armature 0 and its front contact, conductor 14C1, off normal springs 273 and 272, winding of the vertical magnet 261 of the auxiliary connector H, conductor 123, front contact and armature 47, conductor 122, and thence through the winding of the slow acting relay 202 to battery. The above is the circuit over which the first impulse to the vertical magnet 261 is transmitted. Upon the first vertical step of the shaft, the off normal springs are operated and the remaining impulses to the vertical magnet traverse a different circuit which is the same as the one previously traced except that it includes the off normal. springs 273 and 27 i, and armature 220 and its front contact, relay 202 being new in its operated position. Magnet 261 operates to raise the switch wipers 280 283, inclusive, step by step until they are placed opposite the level of bank contacts in which is located tical magnet 261 and maintains its arma tures attracted throughoutthe vertical movement of the switch and at 1S terminaclusive.

pulse of current over the following circuit: From 'round b wa of armature 27 and 1 its back contact, armature 26 and its front contact, armature 1-0 and its front contact, conductor 1&1, oft normal springs 273 and 274, armature 226 and its back contact, conductor 120, working contact of off normal springs 71 and the said spring, conductor 121, back contact and armature 230, where the circuit divides one path extending through the winding of the slow acting relay 204 to battery by way of armature 220 and its bacl: contact; the other path extending by way of conductor 135, armature l9 and its front contact, conductor 13%, off normal spring 271 and its working contact,

armature and its baclr contact, and

thence through the winding of the rotary magnet 202 to battery. l he rotary magnet 262 operates to rotate the switch wipers 280 283, inclusive, step by step until they are placed into engagement with the set of contacts in which is terminated the line o the called substation and which we will assui'ne are the bank contacts 293296, in-

The slow acting relay 204 is energized in multiple with the rotary magnet and operates to connect the test'wiper 282 to the test relay 203 at armature 237.

Should this called line be busy at this time there will be a ground potential pres ent upon the test contact 295 engaged by the test wiper 282. A circuit will then be completed extending from the said grounded test contact by way of the test wiper 282, normally closed springs controlled by armature 252, armature 237 and its front contest relay 203to battery. The relay 203 is energized over this circuit and upon operating establishes a'locking circuit for itself at armature 232 which extends from ground on release trunk conductor 115, off normal spring and its Working contact, conductor 114, of? normal spring 268 and its working contact, normally closed springs controlled by armature 225, armature 232 and 'its front contact, normally closed springs controlled by armature 237 and'through' the winding of the test relay 203 to battery. Relay 203 upon energizing, also places the busy tone uponthe calling subscribers line over a circuit extending from the busy machine by way of front contact and armature 233,

tact, and thence through the winding of the armature 227 and its back contact, eo'nduc tor 126, and thence to the lowertalkin'g'eom 'ductor 6. This tone is audible to the calling subscriber 1n the main exchange and to the called subscriber at substation A. The first called subscriber may now communicate with the original callingsubscriber in order to ascertain whether or not he desires to obtain connection with another subscriber in the branch exchange. Should this be the ase the called subscriber at substation A 'will replace his receiver upon the switch;

hook thereby opening the'circuit of the slow acting relay 12; The circuit of the super-" visory control relay ll'will not be opened at this time as there is alo king circuit com-j pleted for'the relay 17 immediately upon the auxiliary connector H stepping off norma'l'and as this relay completes a circuit of the supervisory control relay 11 the latter relay will'not be deenergized "at this time.

win'ding of the relay 17 to battery. Relay 17 upon energizing, establishes a locking cir cuit for'itself at armature 19 which extends from ground on release trunk conductor 115 by way of armature 242 and its back con-- tact, conductor 141, armature 19 and its front contact,and thence through the winding of relay. 17 to battery. Relay 17 upon operating, also completes the locking circuitof the supervisory control'relay 11. This extends from ground by Way of front con-f tact and armature-18, front'contact and" armature 22, and thence through the winding' of the slow acting'relay 11 to battery.

The slow acting relay 12'upondeenergiz1ng completes a circuit which extends from ground by way of'armature 27 and its back contact, armature 26 a'ndltsback contact, armature 37 and its front contact, conductor 127, armature 253 and its back contact," V I -tion A it will now be assumed that this working contact of 'ofi normal spring 270 and the said spring, and thence through the winding of the release magnet 260' to'battery. Magnet 260'operate's' to restore the auxiliary dual connector H to normal. Iininediately upon the off. normals ring 268 breaking'a'way from its working contact the circuit of the test relay 203 is opened and this relay then deenergizes removingthe' busy tone from the calling subscribers line. The called subscriber at substation Ainay.

now take off his receiver and operate his calllng device in accordance with the digits 'of the number of thenext subscriber desired. The auxiliaryconnector H will be 'oper ated'in'the same manner as was before de- "scribed into connection with the'line.

Returning now to the operation of the auxiliary connector-H when a busy line was encountered its operation will be described when the busy line cal-led wa's one of a group of lines. Under these conditions when the wipers 280-283,- are rotated into engagement with the bank contacts 293296, in-

clusive,there will be a ground potential present uponboth test contacts 294 and 295. The test relay 208 will be energized and Will operate to establish a locking circuit for itself and to prepare the circuit of the step ping relay 201. Following the deenergization of relay 204, a circuit may be traced extending fromthe said grounded test contactf294','test"wip'er 281, armature 251'and its back contact, armature 285 and its back "contact, conductor 131, armature 51 and its front contact,conductor 182, back contact and armature 277, front contact and, arn iature 231, through the winding of the stepping relay 201 and through the winding" of the slow acting'relay 202 to battery." 'Relays 201' and 202 are'ene'rgized over this circuit. Relay 201' upon operating, establishes a loclring circuit for itself at armature 218 and at armature 219 completes a circuit extending from'ground, by way of front contact and armature 219, conductor 135, armature 49 and its front Contact, conductor 134, oif'normal spring 271 and its. working contact, armature 254 and lts'back contact, vanl through the. windingof the rotary magnet 262 to battery. Magnet 262 will operate to rotate the switch wipers 280- 283, inclusive,

'into'enga'gement with the next set ofbank; contacts and to break the locking circuit of the r'el'ays 201 and 202 at armature 277. Re-

lay 1 will immediately deenergize break ing the circuit of the'rotar'y magnet which deenergizes also. The further operation of Returning nowto the operation ofthe a 2:

iliar connector switch H when connection was made with the line of the called substaline was idle. Under these conditions, there will be no round ot-entia-l resent u ion the,

test contact 295. engaged by the test wiper 282 and no circuit, will be completed for "the test relay 203. I Then, renewing the deenergization ofthe slow acting relay 204, a

circuit may be traced f extending from ground on release trunk con ductor'115 by way or off normal spring and its working Contact, conductor 114, off normal spring 268 and its working contact, normally closed springs (ontiolled by armature 225, armature 232'fan d its back contact, upper winding .ofthe switching relay 206, conductor 139,

front contact and {armature 48, conductor .136. back contact andarmature23'r", norma'lly closedsprings controlled by armature 252, test 'wiper282, test contact 295, windmg of the switching relay 2980f the ,line switch.

C, and through 'the win dingbf the stepping magnet299 to battery, Relays 266 andj298 are energized over this circuit.

However, due to a mechanical interlocking" deuce controlled by the armature of the line relay, switching relay 298 is only partially operated in order to disconnect the line of "the-called substation A from its normal switch 'o,

establlshes lfoclf ng c rcuit for'itseli' at battery jand' ground connections in the line Relay 7 206 upon. energ zing,

"armada; 2'55 ,f'over a circuit that extends battery. Relay 206 upon Operating, also Completes the ringing circuit of the called subscriber at substation A whereby ringing current is intermittently projected over from groundon release trunk conductor 101 by way armature. 266 and its back contact, armature 255 and its front contact, and through the winding of relay 206 to called liiie 'until an answer is obtained.

\Vheri this occurs a circuit of the ring cut off relay will be completed. This relay upon energizing establishes a locking cir- Cult for itself at armature 2 11 and at arma tures 24O and 24 opens the ringing circuit and at the front contacts of these armatures finally completes the talking connection. Another result of the energiz ation of relay 205 is that a circuit is completed extending from ground by way of front contact and armature 35, conductor 129, front contact and. armature 24 1, armature 265 and its back contact, conductor 116, off normal spring 72 and its working contact, and

throughthe winding of the release magnet 62 to battery Magnet 62 operates to re-' storethe"main connector H to its normal. position. rn agnet operating the locking circuits of "thering-cut oifr'elay 15 and the switching Immediately upon the release "relay 16"ar'e opened and the switch wipers 8083, inclusive, are disconnected from the talking conductors ofthe main connector.

Before proceeding further it will be neces sary to know certain adjustments of the armatures on the ring out off relay 205; the

armature 24AE is adjusted to close its working Contact a short interval before the armature 243 engages its working contact. This proing contact of off normal spring 270, and

thence thro'ugh the winding of the release magnet 260 to battery, thereby securing the release of. the main connector Hand prearmature 38 is adjusted to engage its working contact a shortinterval before the armature 35 ,eng ages its workingcontact. This is in order to secure the'release of the auxlhary connector H when a call s being transferred from a subscriber called by the auxiliary connector H to subscriber called by means of the main connector H whenthe last called party answers.

l Should the subscriber at substation A re place his receiver upon the switshhook after connection is made with. the line of the substation A and beforethat subscriber answers, the back bridge relay. 13 will be deencrgized andthelcircuit of the slow. acting relay 12 opened. A circuit may then be traced extending from ground by way of armature 2? 'and its back Contact, armature 2 6 and its back 'contact, .arma ture 37 and its front contact, conductor 127, armature 253 and itsfront contact,.conductor 116, oft normal spring 72 and its working. contagt, and thence throughthewinding of the release vmagnet 62 to battery. .The main connector H isthereuponreleased, t will be noted thatupon the back bridge relay 13 deenergizing, the original energizing circuit of the supervisorycontrol relay 11 is opened. Howeventhisi relay does not deenergize at this timefor the. reason that its locking circuit is completed by vrelay 17 which ,is now energized.

, Returning ,now 'to the, operation ofthe auxiliary connector H when the ring cut on relay205 energized the locking circuit of the relay 17 was opened at armature 242 and this relay then deenerg zed, opening the locking circuit of the supervisory control relay ll but the latter relay does not deenergize at this timefor the reason that a circuit is completed by the. back bridge relay 13 which is energized over the line loop of the called subscriber at substation A. Conversation may now becarried on over the heavytalking conductors, between the original callingsubscriber inthe i'nain exchange and the called subscriber at substation A battery being supplied tothe callingsubscriber from the windings of the line relay of the selectorrepeater in the main exchange and to the called subscriber from the windings of thcback bridge relay 13. When the conversation is terminated the release of the dual switches will take place in the same manner as was before described.

Inorder to describethe operation of the dual. switches when the call istra nsferred by means of the main connector H it will be assumed that thei subscriber -at substation A desires to transfer the call to another party in the branch exchange. in order to do this he willl operate 'his calling-device in accordance with the digits of this local subscribers number. Upon. tle operation of the calling device at substation A,

a series of interruptions is produced in'the' circuit of the. back bridge relay 13 which 7 l A deenerg zes a corresponding number or cal magnet. Upon the first vertical step oi the switch the o5 normal sprin s, are operated and the remaining impulses to the vertical magnet travel over a new circuit which is the same as that previously traced except that it includes the off normal springs Hi and (o, conductor 118, armature 226 and its front contact, and conductor 1-17,

relay'202 being in an operated position. The vertical magnet operates to raise the switch wipers 83, inclusive, step by step until they are raised opposite the levelot bank contacts in which is located the bank contacts associated with the line of the de: sired substation. Slow acting relay 202 is energized inv series. with the Vertical magnet and maintains its armatures attracted throughout the vertical movement of the switch and upon its termination deenergizes and transfers the impulsing circuit to the rotary magnet 61. Upon the first vertical step 01 the main connector H a circuit may be tracedextending from ground on release trunk conductor 115, armature 33 and its back contact, working contact of 01? normal spring 69, and the said spring, conductor- 141, working contact of'off normal spring 269 and the said spring, conductor 125, normally closed springs controlled by arma ture 19, and thence through the winding of. relay 1? to battery. Relay 17 upon energizing, establishes a locking circuit for itself at armature 19 and at armature 18 completes a locking. circuit of the supervisory control relay 11. In this manner the super: visory control relay 11 is locked energized until the subscriber called by means oi? the main connector H has answered.

The subscriber at substation A may now operate hiscalling device in accordance with the next digit of his desired number. As before, aseries of interruptionsis produced in the circuit oi the back bridge relay 13 andit deenergizes a plurality of times in response thereto. armature 27 a circuit may be traced extending from ground by way of armature 27 and its back conta ct,-armature 26 and its front At each retraction. of its.

contact, armature 40- and it back contact, ofi normal. springs 74 and 75, conductor 118, armature 226 and its back contact, conductor 120, working contact of oil normal spring 71 and the; said spring, conductor- 121, back contact and, armature 230, conductor 135, armature 49, and its back contact, and through the winding of the rotary magnet 61 to battery. Magnet 61 operates to rotate the switch wipers 80-83, inclusive, into engagement with the set oi bank contacts associated with the desired line. Slow acting relay 20 i is. energized in multiple with the rotarymagnet and. operates. to connect the test wiper 82, to the test relay 203. It will be assumed that the line of the called substation is idle. Under these conditions there will be no groundpotential present upon the test contact engaged by thetest wiper 82 and following the deenergization of the slow acting relay 204: a circuit is completed. extending over the following path: From ground on release trunk conductor. 11 5, cit normal spring 70 and its nemcontact, conductor 114, off normal,

spring 268 and its working contact, normah ly closed springs controlled by armature 225, armature 232 and its back contact, coirductor 138, upper winding of the switching relay 16, back contact and armature 48, con ductor 136, back contact and armature 237, conductor 1. 10, normally closed springs con,- trolled by armature 53, test wiper 82, test contact of the called line, through the winding of the switching. relay of the lineswi' associated with the called substation and thence through the winding of the stepping magnet to battery. The switching of the called line switchoperates toclearthe called line of its normal battery andground connections, Relay, .16 upon energizing, establishes a locking circuit for itself at-arina ture 50 and at armatures e5'and 52 completes. the. ringing circuit. Ringing current is'now projected out over'the called line-in the same manner as was before described. When an answer is obtained ring out off relay 15 is energized. and acircuit is completed extending from ground by way of back contact and armature 66, arinature38 and its frontcontact, conductor 128, armature 243- and its front contact, working contact of off normal spring. 270 and the said spring, and through the winding of the release magnet 260 of the auxiliary connector H to battery. Release magnet 260 upon operating, restores the auxiliary connector H ,to normal. Helay 15 uponenergizingalso opens the lock,- ing circuit: of the relay 17 at armature33. Conversation may now take placebetween the calling and called subscribers over the heavy talking conductors and when thisis,

terminated both parties will replace their connector H will be released upon the calling subscriber replacing his receiver upon the switch-hook in the usual manner.

Had the called line been busy when the main connector H was operated into engage ment therewith the same operations would take place as was described before.

As before mentioned the incoming trunk line comprising conductors 5 and 6 is a two way trunk line and may be used for outgoing calls to the main exchange. hen this trunk line is seized by a local connector selector repeater ground is placed on the release trunk conductor 101 which extends by way of armature 217 and its back contact, conductor 112 through the winding of the cut off relay 10 to battery. Relay 1O energizes and disconnects the incoming trunk line from the dual connectors H and H and transfers it to the outgoing multiples 100 and 102. A call may now be made over the trunk-line in the usual automatic manner which need not be described.

Having described the operation of the dual connectors H and H, Figs. 1 and 2.. the operation of the modification shown in Figs. 3 and 4 will now be discussed. For this purpose it will be assumed that a calling subscriber in the main exchange desires to call the substation A in the private automatic exchange, and it will be assumed further that he has operated various switches in the main exchange and finally connected to the trunk line comprising conductors 305 and 306 which terminates in dual connectors H and H in the private automatic exchange. When this occurs the circuit of the line relay 314 will be completed over the two sides of the incoming trunk line in series. Relay 314 upon energizing, completes the circuit of the slow acting release relay 315 which operates to prepare the impulsing circuits of the main dual connector H at armature 337 and at armature 338 grounds the release trunk conductor 376 whereby the multiples of the incoming trunk line in the banks of the local connector selector re peaters are busied in order to prevent their seizure for outgoing calls to the main ex change. 7

The calling subscriber may now operate his calling device in accordance with the next digit of the desired called subscribers number. By this operation a series of interruptions is produced in the line relay circuit which deenergizes a corresponding number of times each time sending an impulse of current over the following path: Ground by way of armature and its back contact, armature 337 and its front contact, off normal springs 36S and 357, winding of the vertical magnet 357, back contact and armature 328, conductor 417, and thence through the winding of the slow acting relay 513 to battery. The above is the circuit over which lng impulses to the vertical magnet traverse a new circuit which is the same as the one previously traced except that it includes the oil normal springs and 369, conductor 421, armature 531 and its front contact, and conductor 422, relay 513 being new in an operated position. The vertical magnet 357 operates to raise the switch wipers 380-383, inclusive, step by step until they are placed opposite the level of bank contacts in which is located the contact set associated with the line of the substation A The slow acting relay 513 is energized in series with the vertical magnetand maintains its armature attracted during the vertical movement of the switch and at its termination deenergizes transferring the operating circuit tothe ro tary magnet 355.

The calling subscriber in the main exchange may now call the next and final digit of his desired number. 'As before, the line relay 314 retracts its armature a plurality of line circuit. n each retraction of its armature 334 an iaioulse of current is sent over a circuit extending from ground by way of armature 334 and its back contact, front contact andarnlature 337, oti normal springs 368 and 369, conductor 421, armature 531 and its back contact, conductor 420, working contact of off normal spring 366 and the said spring, conductor 432, armature 541. and its back contact, where the circuit divides one path extending through the winding of the slow acting relay 516 and thence to battery by way of back contact and armature 52'? and the other path extending over conductors 429, armature 349 and its back contact, and through the rotary magnet 355 to battery. Magnet 355 operates to rotate the switch wipers step by step until they are placed in engagement with the set of bank contacts associated with the line of the called substation A which we will assume the bank contacts 386389, inclusive. Slow act ing relay 515 is energized in multiple with the rotary magnet and operates at armature 546 to connect the test wiper 382 to the test relay 515.

hould the desired line be busy there will be a ground potential present upon the test contact 388 and the testrelay 515 will be energized. Belay 515 upon energizing, establishes a locking circuit for itself at its armature 540 and at armature 543 places the busy tone on the line of the calling subscriber. Upon hearing this tone the calling subscriber will replace his receiver upon the switchhook and the main dual connector H will be released in the usual manner.

Should the calling substation A be one in a group of telephones listed under one 110 times in response to the interruptions in its.

described in connection with themain dual connector H, Fig. '1.

It .will now be assumed thereto was attempted. Under these conditions the test contact 388 will be un--- ti re328fconductor 417, and'thencethrough the winding of 'the slow acting relay 513' to Theabove is the" circuit over which"thefirstfimpulseto the vertical mag net 561 'is'i'siit. Upon'the' first "vertical step grounded and no circuit will" be completed for the test relay 515. Then, tollowingthe; deenergization of the slow acting relay-516,]

a circuit will be tracedextending from ground on release trunk conductor 307 by way of on? normal spring 364 and its work ing contact, conductor 418, off normal spring 565 and its'resting'contact, normally closed springs controlled by armature 530, arma ture 540 and its back contact, conductor 438, upper winding of the switching relay 317, back contact and" armature 342, conductor 430, back contact and armature 546, conduc-v tor 437, normally closed springs controlled by armature- 351, test Wiper 382, test' contact 388, through the winding of the switching relay 95 oi the line switch C and through the winding of the stepping magnet'396 to battery. Relays 317 and 395 are energized over this circuit. The switching relay 395 is only'partially operated, thatis, enough to disconnect the line of the called substation from its normal battery and ground connections in theline switch C Switching relay 317 upon energizing, establishes a locking circuit for itself at armature 352 and at arinatures 348 and 353 completes the ring-' ing circuit. Ringing. current is intermittently projected over the line of the substation A Then the called subscriber answers the ring out ofi relay 316 will be energized over the line of'the calldsubscriber. Upon operating relay 316'at armature 343 establishesa locking circuit for itself and at armatures 340 and 345 opens the ringing circuit and at the front contacts of these armatures finally completes the talkingv connection. The back bridge relay 313 is also energized over the called subscribers line loop. Upon operating, this relay completes the circuit of the slow acting relay 312 and that of the slow acting supervisory control relay 311. Relay 312 operates to prepare the impulsing circuit of theauxiliary connector H and relay 311 operates to reverse'the battery over the incoming trunk line whereby an operator is given supervision or a metering device at the calling substation operated.

Should the called subscriber at substation A find it desirable to call another party in the branch exchange he will operate his calling device for the digits of the subscribers number. By, the operation of the calling device at substation A a series of inter ruptions is produced inthe circuit of the I that the line of the substation A was idle when connection backbridge relay 313 which deenergizes a plurality of times"in responsethereto? '1' each 1 deenergiz'ation' an impulse" of current is" sent over the following. path: From ground by way? of 5 armature 1 332. and its baekeontact,"armaturesao and its front con-'1 tact," conductor 440, 0a normal springs 57 0 f and" 569, windingfo'f the vertical" magnet 561, conductor 119';frontcontaetandarma:

battery;

oftheauxiliary'. connector H th'ekfil' normal springs arejshitted' and the remaining imcorresponding to the digit calledg Slow acting "relay 513 is energized in serieswith the vertical magnet and remains so througlr' out the verti'cal' operation otthe switch. Shortly after the"terminationbfthe opera-f tion or the vertical magnet the'slow' acting" relay, 513 deenergi'zes and transfers-the'imgl pulsing. circuit 'to' the rotary magnet 562;

Thecalle'd subscriber at substation- A may now operate" hiscallin'g device in acco'rdan'ce with thelast digitof thefde'sire'd' subscribers number. The back bridge re lay 313 responds'to the'interrupt'ions in its line circuit and will deenergiz'e' a plurality of iti'mes,feach time sending an impulse of current over" a' circuit' extending ground by way "ofar'mat'ur'e" 332 and it's back contact, armature 330" and its front contact, conductor 440," off" normal springs 57 O and 571, armature 531 and its back con;

tact, conductor 42() working contact 0f 'ofi' normal spring 366 and the said spring,conductor 432, armature 541 a nd'its back contact, conductor 429, armature 349"andits front contact, conductor j435, oflinormall" springf567 and its working'conta'ct, ar1na-' ture 555 and its back contact," and through the Windingfof the rotary magnet 562 to battery. Magnet 562 operates to rotate the Wipers 580-583, inclusive, into engagement with the set of bank contacts associatedwith the line of the called substation which we will assume are the bank contacts 585 588, inclusive, I associated with the line of the substation A Slow acting relay 516 is energizedin inultilalWithth rotary magnet and operates to connectithe test Wiper 582' to they test'relay 515. L V

Assuming that the desired lineis idle there willb e. no ground potential present upon the testcontact" 587 and consequently from f i noeircuit will be completed for the test relay 515. Then, following the deenergization of the slow act-ing relay 516, a circuit is completed extending from ground on release trunk conductor 307, 06 normal spring 364 and its working contact, conductor 418, off normal spring 565 and its working contact, normally closed springs controlled by armature 530, armature 540 and its back contact, upper winding of the switching relay 517, conductor 436, front contact and armature 342, conductor 430, back contact and armature 546, normally closed springs controlled by armature 552, test wiper 582,

test contact 587, winding of the switching relay 590 of the line switch C and through the winding of the stepping magnet 591 to battery. Relay 590 upon operating, clears the line of the called substation from its normal battery and ground connections in the line switch C Relay 517 upon energizing, establishes a locking circuit for itself at armature 553 and at armaturcs 550 and 556 completes the ringing circuit whereby the called subscriber is intermittently signaled. When the called subscriber at substation A removes his receiver from the switchhook, ring out off relay 514 will be energized. Upon operating, this latter relay completes a locking circuit for itself at armature 536 and at armatures 534, and 538 completes the talking connection. The back bridge relay 511 is also energized over the line loop of the called subscriber and operates to complete the circuit of the slow acting relay 510 and also that of the super visory control relay 311. Relay 510 upon energizing, completes a circuit extending from the tone machine, front contact and armature 329, conductor 415, armature 521 and its front contact, lower Winding of the back bridge relay 511, and thence to the lower talking conductor of the auxiliary connector II. This tone is audible to the two called subscribers and serves to inform them that there are three parties on the line. This provision is made so that one called party cannot remain on the line without the knowledge of the other subscriber. It willalso be noted that upon the first off normal step of the auxiliary connector H the relay 318 is energized and it establishes a locking circuit for itself at armature 320 and at armature 319 completes the locking circuit of the supervisory control relay 311. The called subscriber at substation A is therefore able to replace his receiver upon the switchhook without restoring the normal polarity of the battery over an incoming trunk and thereby preventing it from giving a disconnect signal to an operator if one is included in the connection. Conversation may now be carried on between the subscribers over the heavy talking conductors.

Should the subscriber at substation A at any time desire to retire from the connection 7 contact, conductor 433,armature 554 and its front contact conductor 427, working contact of off normal spring 365 and the said spring, and thence through the winding of the release magnet 356 to battery. Magnet 356 operates to restore the main dual connector H to normal. Immediately upon operating the release magnet also opens the locking circuits of the ring cut off relay 316 and the switching relay 317.

Should the called subscriber at substation A desire to disconnect himself from the connection he may do so by replacing his receiver upon the switchhook. The back bridge relay 511 is then deenergized and the circuit of the slow acting relay 510 is'opened. Upon the deenergization of the latter relay, a circuit is completed extending from ground by way of armature 522 and its back contact, armature 520 and its back contact, front contact and armature 537, conductor 425, armature 350 and its front contact, conductor 426, working contact of oif normal spring 568 and the said spring, and thence through the winding of the release magnet 560 to battery. Magnet 560 operates in the usual manner to restore the auxiliary connector H to normal and the subscriber at substation A is accordingly released from the connection. Should the line of the called subscriber at substation A5 be busy or should the calling subscriber at substation A desire for any reason to release the auxiliary connector H prior to the time connection was made to the line of the called substation he would rep-lace his receiver upon the switchhook, the relays 313 and 312 would deenergize, and a circuit would be completed extending from ground by way of armature 332 and its back contact, armature 330 and its back contact,

front contact and armature 344, conductor 433, armature 554 and its back contact, working contact of off normal spring 568 and the said spring, and through the winding of the release magnet 560 to battery. Upon the operation of the release magnet the auxiliary connector H would be restored to normal.

Should the subscriber at substation A not desire to hold the line until the answer of the subscriber at substation A he would replace his receiver and the main connector H would be released in the same manner as was described when the subscriber at substation A desired to retire from the three party connection. The normal battery flow over the incoming trunk line would not here stored, however, as at this time the relay 318 would be locked energized as would'the supervisory control relay 311. I

It will now be assumed that after the. subscriber at substation A had retired from the three party connection the subscriber at substation A desired to call another party 'for the calling subscriber. In order to do this he would operate his calling device for the digits corresponding to the number desired. By the operation of the calling device-at substation A a. series of interruptions is produced in the circuit of the back'bridge relay 511 which deenergizes a plurality of times in response thereto each time sending an impulse of current over the following circuit: From ground'by way of armature 522 and'itsback contact, armature 520 and its front contact, conductor 4'13, off normal springs 36S" and 367, winding of the vertical magnet 357, back Contact and armature 328, conductor 417, and thence through the winding of the slow acting, relay 513 to battery. Upon the first vertical step of the switch the oil normalsprings are shifted and the re main-ing impulses to the vertical magnet travel over a. new circuit which is the same as the one traced-above exceptthat it includes the off normal'springs 368 and 369, conductor 4:21, armature 531 and its front contact, and conductor 4:22, relay 513 being now energized. Magnet 357 operates to raise the switch wipers of the main dual connector opposite the level'of the bank contacts in which is located the contact set associated with the line of the desired substation. Slow acting relay 513 is energized throughout th vertical moVc-ment'ofthe switch and at its termination dcenergizes transferring the impulsing circuit to the rotary magnet 355.

The subscriber at substation A may now operate his calling device in accordance with the final digit of the-desired subscribers number. Back bridge relay 5311 again responds to the interruptions inits line circuit each time sending an impulse of current over the following path: From ground by way of armature 522 and its back contact, armature 520 and its front contact, conductor 413, off normal springs 368 and 369, conductor e21, armature 531 and-its back contact, conductor L20, working contact ofoff normal spring 366 and the said spring, conductor armature 5-11 and its back contact, conductor 429, armature 3 19 and its back contact, and through the winding of the rotary magnet 355 to battery. Magnet 355 operates to rotate the switch wipers 380383, inclusive, into engagement with the contact set associated with the line of the called substation. The slow acting relay 516 is energ zed in multiple with the rotary magnet and operates to connect. the .test wiper 382 to the test relay 515.

Should the desired line be busy there will be a ground potential upon the test contact engaged bytest wiper 382 and the test relay 515' will be energized and the busy tone given to the subscriber. Should the line or this called substation be one of a group of lines the automatic operation of the connector H by which an idle line is selected will take place in the same manner as was described hereinbefore.

Assuming that the desired called line is not busy there will be no ground potential upon this test contact and no circuit will be completed for the'test' relay 515. The subsequent operations of the main connector H by which the called subscriber is signalled and the connection released will take place in the usual manner. It will be noted that upon the first off normal step of the connector H that the relay 318 is en'- ergized and operates to control the supervisory relay 311 in the same manner as before.

As before mentioned, the incoming trunk line comprising conductors 305 and 306 is a two Way trunk line and is adapted to be seized by a local connector selector repeater. WVhen this occurs ground will be placed on release trunk conductor 376 which extends by way of armature 338 and its back contact, through the winding of relay 310 to battery. The relay 310 is thereby energized and operates to disconnect the trunk line comprising conductors ,305 and 306 from the dual connectors H and H and transfers it into connection with the local connector selector repeater. The trunk line may now be used for a call to the main exchange in the usual manner.

Having fully de'scribed'an'd ascertained the features ofthe invention, what is conlines, a relay common tosaid automatic connector switches, and'means for energizing said relay only during the rotationof whichever switch is being operated for initiating thB'TGStIHg of said called line.

2. In a telephonesystem, automatic connector switches, called linesaccessible to said SWltChCS and cl-ivide'dxinto groups, means for operating either oneof said switches in accordance with-the two final digits in a called telephone numberto select a desired group of llIlGS, and means-including relay mechanismxcommon to said switohes for causing the=operated connector switch to select the first idle line in theselected group.

3.111 a telephone system, a plurality of" subscribers lines, a pair of connectors adapted to establish connection with said lines, reiay mechanism common to said connector sw ches, said relay mechanism being normally adapted to control the operation of the shaft and wipers of a particular one of said connectors in accordance with a digit in a telephone number "for establishing a connection with line, and means for then disconnecting the relay mechanism from the operated switch and connecting it with the other connector switch while the first is maintained in operated position.

4.. in a tele hone system, a pair of automatic connector switches, called lines acces sible thereto, means for operating one switch of said pair into connection with one of said called lines, means controlled by the subscriber on the connected called line tor then operating the other switch of said pair into connection with another of said called lines, the control being exercised over a circuit including wipers of said first switch, and a relay common to said pair of switches for supplying tailing current to each of the subscribers on said called lines.

5. In a telephone system, a pair of automatic connector switches, called lines accessible thereto, means for operating one switch of said pair into connection with one of said called lines, means controlled by a subscriber on the called line for then operating the other switch of said pair into connection with another of said called lines while maintaining the first switch in operated position, and a busy test relay common to both switches of said pair for testing said called lines.

6. In a telephone system, a pair of automatic connector switches, called lines accessible thereto, means for operating one switch of said pair into connection with one of said called lines, means controlled by the subscriber on the connected called line for then operating the other switch of said pair into connection with another of said called lines, the control being exercised over a circuit including wipers of said first switch, a relay common to said pair of switches for supplying talking current to each of the subscrihers on said called lines, and a second relay energized upon the operation of said common relay for controlling supervision.

7. In a telephone system, a pair of automatic connector switches, called lines accessible thereto, means for operating one switch of said pair into connection with one of said called lines, means controlled by the sub scriber on the said called line for operating the other switch of said pair into connection with a second called line, means for applying ringing current to the second called line, a relay energized upon the response of the second called subscriber for disconnecting said ringing current, and a release circuit completed by the operation of said relay for releasing the firstswitch of said pair.

8. In a telephone system, called subscribers lines, a pair of automatic switches having access to said lines, means tor ope "ating one of said switches into connection with one of said lines, means under the control of the subscriber on the said called line for operating the other of said pair of switches into connection with another of said lines, the control being exercised over a circuit including the wipers of said first switch, a test relay common to both of said connector switches and means for operating said relay when either of said pair of switches engages a busy called line.

9. In a telephone system, a pair of automatic connector switches, calling and called lines, means under the control of a subscriber on one of said calling lines for operating one switch of said pair into connection with one or said called lines, a relay energized upon the response of the subscriber on the said called line for reversing the direction of current flow over the said calling line, means under the control of the subscriber on said called line for operating the other switch of said pair into connection with another of said called lines, a second relay energized upon the operation of said second connector switch for closing a locking circuit for said first relay, and means for opening said locking circuit upon the response of the subscriber on said second called line.

10. In a telephone system, an automatic connector switch, called lines divided into groups accessible thereto, a test wiper or said switch, means for operating said switch vertically and for rotating it into connection with one of said called lines, a relay, a second relay energized during the rotation 0t said switch for connecting said test wiper to said first relay, a second test WlPl.'fOl' said switch, means controlled by said second test wiper for initiating an automatic rotation of said switch it said connected called line is busy, and means for opening the circuit of said second relay in order to prevent its energization during the automatic operation of said switch.

11. In a transfer call system, a main connector for extending a connection to a called line, an auxiliary connector controlled by the subscriber on the called line for passing the call from said called line to a second called line, operating magnets for each connector, and a relay common to said connectors for shifting the operating circuits of either connector when the same is operated.

12. In a transfer call system, a main connector for extending a connection to a called line, an auxiliary connector controlled by the subscriber on the called line for-passing the call to a second called line, primary and secondary operating magnets in each connector, an operating circuit, and a relay effective when either connector is being operated to shift the operating circuit from the primary magnet to the secondary magnet.

13. In a transfer call system, a main connector for extending a connection to a called line, an auxiliary connector controlled by the subscriber on the called line for passing the call to asecond called line, primary and secondary operating magnets in each connector, and a common stepping relay for controlling the secondary magnets of both switches.

l l. In a transfer call system, a main connector for extending a connection to a called line, an auxiliary connector controlled by the subscriber on the called line for passing the call to a second called line, primary and secondary operating magnets in each connector, circuits for automatically operatin the secondary magnets, and a plurality of common relays for controlling said circuits.

15. In a transfer call system, a main connector for extending a connection to a called line, an auxiliary connector controlled by the subscriber on the called line for passing the call from said called line to a second called line, a test relay common to said con nectors, and circuit connections for operating said relay in case either called line is busy.

16. In a transfer call system, a main connector for extending a connection to a called line, an auxiliary connector for passing the call to a second called line, a test wiper for each connector, and a conductor normally conductively connecting said wipers directly together. I

17. In a transfer call system, a main connector for extending a connection, to a called line, an auxiliary connector controlled by the subscriber on the called line for passing the call to a second called line, a battery feed relay common to said connectors, circuit connections from said relay for supplying current to the first called line'before the call is passed and for supplying current to the second called line after the call is passed.

18. In a telephone system, a pair of automatic connector switches, called lines accessible thereto, means for operating one switch of said pair into connection with one of said called lines, means for then operating the other switch of the pair into connection with a second called line, means for applying ringing current to the second called line, a

relay energized upon the response of the second called subscriber fordisconnecting said ringing current, and a release circuit completed by the operation of sa1d relay for releasing the first switch of the pair.

19. In a telephone system, called lines, a pair of connector switches, means for operating either switch into connection with one of said called lines, means for thereafter operating the remaining switch into connection with another one of said lines, means for applying signaling current to the last called line, and a relay operative upon the response of the second called subscriber to cut oif the signaling current and to close and release circuit of the first operated switch.

20. In a telephone system, calling and called lines, a pair of connector switches having access to said called lines, means for setting up a connection to one of the called lines via one of said switches, means for then transmitting signaling current to the line called, a relay in the switch used operative upon the called subscriber responding to cut off said signaling current and to close a point in its own restoring circuit, means for then operating the second switch of said pair to establish a connection with a second 7 called line, and a corresponding relay in the last operated switch operative contingent upon a response being received over the last line called to complete the restoring circuit. I 21. In a telephone system an established connection between a calling and a called line, the connection including one of a pair of automatic switches, means under the con trol of one of said lines for causing a connection to be established between the other line and a third line, said connection including the other automatic switch, release circuits for said automatic switches, and means operative contingent upon a response occurring on the second called line for completing said circuits. V

22. In a telephone system, calling and called lines, a pair of automatic switches having access to certain of said lines, means for completing a talking connection between calling and called ones of said lines, means controlled over one of the lines in the established connection for establishing a talking connection between the other line and a second called line, restoring circuits for said switches, means for closing said circuits. operative upon response of the second subscriber called, and means for preventing the release of the last operated switch at this time.

23. In a telephone system, a trunk line terminating in a pair of directively controlled automatic switches, means for operating one of said switches into connection with a called line, a relay energized upon I the response of the called subscriber to reverse the direction of current flow over said I trunk, means for operating the other switch of the pair into connection with a second line, and a second relay for closing a locking circuit for said first relay responsive to the operation of the other switch.

In witness whereof, I hereunto subscribe my name this 31st day of March A. D.,

JOHN E. GARDNER. 

